This invention relates to a method for making sodium-mercury amalgam pellets for use as a part of the discharge sustaining fill of a high-pressure sodium (HPS) discharge lamp.
In the prior art practice the sodium-mercury amalgam used as the discharge sustaining fill in a high-pressure sodium discharge lamp has been delivered to the discharge lamp arc tube as fine salt like granules introduced through the exhaust tubulation at one end of the arc tube body.
In newer versions of the high-pressure sodium discharge lamp, the arc tube body is now constructed without exhaust and fill tubulation and the end closures are ceramic buttons instead of refractory metal end caps with their associated exhaust and fill tubulation. With this configuration, liquid amalgam has been introduced into the open end of an arc tube that has had one end previously sealed. Amalgam heated to a liquid is retained in a reservoir that is pierced by a plunger which has been suitably notched to form a cavity for the required charge of amalgam. Motion of the cavity into and out of the liquid measures the droplet that enters the arc tube. The introduction of amalgam is more readily and reliably preformed if the amalgam is in the form of a pellet of predetermined weight.